The present invention relates to a spacer-damper for bundled conductors of electric lines and, more particularly, to such a device which is capable of substantially damping the movements of the individual sub-conductors from aeolian vibrations. In bundled conductors of high and very high tension electric lines, i.e., conductors composed of two or more sub-conductors for each electric phase, it is necessary to keep the correct mutual spacing of the sub-conductors along each span between adjacent towers as well as along the entire length of an electric line. It is further necessary to substantially damp the movements of the individual sub-conductors from aeolian vibrations, i.e., high frequency and small amplitude vibrations caused by weak winds as well as violent and large amplitude oscillations caused by strong winds.
Spacer-dampers are devices which are mounted on the electric lines in order to meet both of the above requirements. Single joint spacer-dampers are disclosed, for example, in U.S. Pat. No. 3,748,370, owned by S.A.S. Officine Meccaniche Innocente Riganti di Innocente e Franco Riganti & C. of Solbiate Arno, Italy. Multiple joint spacer-dampers are presently manufactured by DAMP of Sovere, Italy and A. SALVI & C. of Milan, Italy.
The principal disadvantage of a single joint spacer-damper such as the one described, for example, in U.S. Pat. No. 3,748,370, is that, due to its reliance on a single joint, each arm is permitted to move only in an angular direction. Since angular oscillations are centered in the joint center, there is no possibility of movement in the direction of the arm axis. The main disadvantage of the multiple spacer-dampers of the two other cited manufacturers resides in the fact that, while they are permitted to move in a number of directions, movement is restricted to the plane perpendicular to the longitudinal axis of the sub-conductors. Moreover, in all of these devices, the rigidity of the joint is nearly constant under aeolian vibrations and, as such, the damping effect depends only on the hysteresis of the elastic means comprised in the joints with almost all of the dissipated energy being transformed to heat which damages the elastic means. Furthermore, as in almost all these devices, the elastomeric elastic means becomes compressed. A further disadvantage associated with such devices is that their performance varies widely depending upon the external temperature at the time.
Finally, the prestresses of the elastic means result in the joints being extremely rigid and, consequently, such devices are not sensitive to small exciting forces.